1. Field of the Invention
The present invention relates to a sample preparation method for forming a deposition film on a sample by irradiation of a charged particle beam.
2. Description of the Related Art
Transmission electron microscope (TEM) observation is conventionally known as a method of observing a micro region in a sample for analysis of defects in a semiconductor device or other purposes. In TEM observation, as sample preparation for acquiring a transmission electron image, it is necessary to prepare a TEM sample having a thin film portion in part, which has such a thickness that allows an electron beam to transmit therethrough.
In recent years, as a method of preparing a TEM sample, a TEM sample preparation method using a focused ion beam has been used. In this method, a peripheral portion of a sample is subjected to etching processing such that a portion including a desired observation region inside the sample may be left. Then, the remaining portion is subjected to etching processing until the remaining portion has such a thickness that allows an electron beam to transmit therethrough, to thereby form a thin film portion. In this manner, a TEM sample can be prepared with pinpoint accuracy with regard to the portion including the desired observation region.
However, there has been a problem in that, in preparing the TEM sample, if the thickness of the thin film portion becomes smaller, the thin film portion is curved due to internal stress. As a method for solving the problem, there is disclosed a method of preventing the curvature by forming a reinforcement layer made of a deposition film on the thin film portion (see JP-A-2009-198412).
According to this method, however, in the case of forming a thin film portion having an extremely small thickness, the thin film portion may be curved by a tension of the deposition film.